In the art of electroplating and electroforming for forming an electrodeposited layer or film on a metallic or metallized substrate or workpiece, it is practically always desirable that the layer or film be formed uniformly on a desired surface area thereof. Depending upon the particular configuration of a selected receiving surface of a workpiece, however, it is generally difficult to assure a uniform distribution of potential gradients over the selected workpiece surface. There are surface areas on which an electrodeposit is barely formed as well as surface area on which the deposit is formed selectively or with a greater rate. The selective or preferential formation of electrodeposit on a certain area in the initial stage causes a further unbalance in the distribution of potential gradients so that in the subsequent stage the deposit is concentrated on that area and practically no further deposit is created on the other areas.
In order to solve this problem, various proposals have been made heretofore and include the use of a plurality of anodic electrodes designed and arranged in accordance with the particular surface configuration of the workpiece, the use of one or more auxiliary electrodes, the controlled delivery of an electrodepositing liquid electrolyte and the use of one or more masking plates in an attempt to create the distribution of potential gradients of a greater uniformity and to locally modify the thickness of the electric double layer.
Not only are these provisions complicated and inconvenient, it has been found that they are completely not satisfactory to produce an electrodeposited layer of uniform thickness depending on the particular configuration of the receiving workpiece surface. Difficulties especially arise in the deposition on a deep recess or a surface including a deep or angularly intended area are, especially uniformly on the entire wall of an angular recess and yet particularly on the bottom wall portion of an angular recess or indented area having an acute cross-sectional angle.